An infection between the skin and the anus.
An anal fistula is an infected tunnel between the skin and the anus. The anus is the muscular opening at the end of the digestive tract. Most anal fistulas are the result of an infection in an anal gland that spreads to the skin.
Symptoms of an anal fistula include an opening on the skin around the anus that may be inflamed or oozing pus, blood or stool.
Surgery is usually needed to treat an anal fistula.